Hydrofluoroolefins (HFOs), such as tetrafluoropropenes (including 2,3,3,3-tetrafluoropropene (HFO-1234yf)), are now known to be effective refrigerants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), both of which potentially damage the Earth's ozone layer, HFOs do not contain chlorine and, thus, pose no threat to the ozone layer. HFO-1234yf has been shown to be a low global warming compound with low toxicity and, hence, can meet increasingly stringent requirements for refrigerants in mobile air conditioning. It has been found to be an effective refrigerant, heat transfer medium, propellant, foaming agent, blowing agent, gaseous dielectric, sterilant carrier, polymerization medium, particulate removal fluid, carrier fluid, buffing abrasive agent, displacement drying agent and power cycle working fluid. Accordingly, compositions containing HFO-1234yf are among the materials being developed for use in many of the aforementioned applications. Thus, there is a need for new manufacturing processes for the production of tetrafluoropropenes and in particular 2,3,3,3-tetrafluoropropene.
Several methods of preparing HFOs are known. For example, U.S. Pat. No. 4,900,874 (Ihara et al.) describes a method of making fluorine containing olefins by contacting hydrogen gas with fluorinated alcohols. Although this appears to be a relatively high-yield process, commercial scale handling of hydrogen gas at high temperature is hazardous. Also, the cost of commercially producing hydrogen gas, such as building an on-site hydrogen plant, is economically costly.
U.S. Pat. No. 2,931,840 (Marquis) describes a method of making fluorine containing olefins by pyrolysis of methyl chloride and tetrafluoroethylene or chlorodifluoromethane. This process is a relatively low yield process, and a very large percentage of the organic starting material is converted to unwanted and/or unimportant byproducts, including a sizeable amount of carbon black which tends to deactivate the catalyst used in the process.
The preparation of HFO-1234yf from trifluoroacetylacetone and sulfur tetrafluoride has been described (See Banks, et al., Journal of Fluorine Chemistry, Vol. 82, Iss. 2, p. 171-174 (1997)). Also, U.S. Pat. No. 5,162,594 (Krespan) discloses a process wherein tetrafluoroethylene is reacted with another fluorinated ethylene in the liquid phase to produce a polyfluoroolefin product.
A manufacturing process for HFO-1234yf, as disclosed in U.S. Pat. No. 8,058,486, uses 1,1,2,3-tetrachloropropene (HCO-1230xa) as starting raw material. The process consists of the following three steps: 1) HCO-1230xa+HF→2-chloro-3,3,3-trifluoropropene (HCFO-1233xf)+HCl in a vapor phase reactor charged with a solid hydrofluorination catalyst such as fluorinated chromia, 2) HCFO-1233xf+HF→2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) in a liquid phase reactor charged with a liquid hydrofluorination catalyst such as fluorinated SbCl5, and 3) HCFC-244bb→HFO-1234yf in a vapor phase reactor. One issue encountered in the operation of Step 2 is the formation of 1,1,1,2,2-pentafluoropropane (HFC-245cb), which can cause significant yield loss in long term. Thus, there is a need for means by which the formation of HFC-245cb can be reduced.